Method of sealing glass windows to metallic cones for cathode-ray tubes



y 1952 J. G. w. MULDER ET AL 2,598,286

METHOD OF SEALING GLASS WINDOWS TO METALLIC CONES FOR CATHQDE-RAY TUBES Filed Aug. 14, 1950 INVENTORS J. G. W. MULDER BY T. HAGENBERG AGENT Patented May 27, 1952 METHOD OF SEALING GLASS WINDOWS TO FOR CATHODE-RAY METALLIC OONES TUBES Johannes Gijsbertus Wilhelm Mulder and Theodorus Hagenberg, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Conn-., as trustee Application August 14, 1950, Serial No. 179,318 In the Netherlands September 10, 1949 3 Claims;

This invention relates to methods of sealing a glass window to a metallic cone of a cathoderay tube, more particularly of a television tube.

In sealing such a window to the edge of a metallic cone, it is important that the sealing process should be accompanied by vigorous measures to ensure that the glass is heated as evenly as possible. Consequently, it has previously been suggested to surround the glass window by a heat radiating screen so that the window is heated indirectly by means of radiation from the heated screen. After the window has reached a temperature of approximately 350, the edge to be sealed is strongly heated by means of an additional burner so that the glass of the edge of the window is sealed to the metal of the cone. The cone is arranged with its wide end at the top, the window being deposited on the edge of the cone. The assembly is continuously rotated in order to ensure uniform heating and to enable the edge to be heated by means of one or more flames. The heating process thus takes place very slowly.

According to the invention, uniform heating is ensured within a comparatively short time and, furthermore, a mechanic simplification is obtained in that rotation of the cone and the window is not required. According to the invention, in a method for sealing together a me tallic cone and a glass window for cathode-ray tubes, more particularly television tubes, in which the cone is arranged with its. wide end at the top and the glass window is deposited thereon, and furthermore the cone is surrounded by a heat radiating screen and heated by radiated heat, part of the cone is surrounded by a high-frequency coil, whilst by mutual displacement of the coil and the cone in the longitudinal direction of the cone, the heated zone of the cone is partly moved from the narrow end to the area of sealing of the window, the temperature of the heated zone being gradually increased so that the window is heated by radiation from the cone so that the edge of the window is sealed to the cone when the said zone has reached the sealing edge of the cone.

The upper face of the window is surrounded by a screen which is heated by radiation from the cone and thus itself heats the upper side of the window by radiation, while the lower face of the window is gradually heated by radiation from the heated zone of the cone. Since the temperature of this zone increases with increase of the diameter of the part of the cone provided within the high-frequency coil, the glass is 2 heated comparatively quickly. The heat radiating screen provided at the upper face of the window is preferably shaped so that it is at all points equally spaced from the glass of the window and the screen can furthermore be blackened at its lower side and made reflecting at its upper side. The screen thus has a low thermal loss due to radiation whilst itself acquiring a high temperature due to the radiation from the cone so that the upper face of the window is likewise heated rapidly by radiation. If desired, the heating of the screen may be accelerated and enhanced by flames directed on to the upper side. An important advantage of heating of the glass by radiation, more particularly in the case of thick plates, consists in that the glass is heated by heat absorption simultaneously at its surface and at the interior so that the stresses in the glass are much smaller than with heating by burners, in which event the glass is heated from the outside towards the interior. Since rotation of the cone is not required, it may be arranged in a stationary holder with its wide end at the top, whilst the high-frequency coil, the height of which is small with respect to that of the cone, is adapted to be moved upwards or downwards. However, as an alternative, it is possible to make the base plate carrying the cone to be movable so as to enable the cone to be moved up and down within the stationary highfrequency coil.

A preferred method according to the invention will now be described in detail with reference to the accompanying drawings, in which:

Fig. 1 shows the arrangement of the cone and the window before sealing and Fig. 2 shows diagrammatically a complete cathode-ray tube.

In Fig. 1, reference numeral l indicates the metallic cone, the upper side of which is provided with a narrow flange bearing the glass window 2. The cone is supported by a holder 3 and closed at its lower side by a rubber stopper which is traversed by a tube through which, in this example, nitrogen is blown into the cone. The cone is partly surrounded by a high-freqeuncy coil 5, which at the beginning of the heating process occupies the position shown near the lower end of the cone. After switching-on the high-frequency current, that zone of the cone which is located within the coil becomes hot and heats by radiation the glass window 2 and, as the case may be, the heat radiating screen I. In order to restrict the thermal losses due to radiation, the screen has a reflecting surface at least on the side remote from the window. However, as a rule, it is desirable that the screen I should be heated additionally by means of a burner, the screen being rotated in order to acquire a uniform temperature. This may be eifected in a very simple manner, as shown in Fig. 1'. The screen I may be provided with marginal radial slits or it may consist of insulating material, in order to avoid overheating due to the high-frequency field of coil 5, when this coil has been moved upwards into the position with respect to the cone. During the gradual upward movement of the coil 5, the temperature of the heated zone becomes higher and higher sincethe metal of the cone in this zone approaches more and more the high-frequency coil. In the position 5', the window 2 is heated to approximately 350'", the flange 6 of the cone being strongly heated so that the edge of the window 2 is sealed to the flange 6. The pressure of the gas which may be admitted. to the cone at its lower side enables the window 2 to be moved into the correct position with respect to the cone, since the window 2 now bears all around on the soft glass edge. When the window has assumed the correct position, the high-frequency coil is rapidly moved downwards so that the glass of the edge of the window hardens. The assembly is then removed from the holder 3 and placed in a furnace to ensure uniform cooling. However, as an alternative, it is possible for the highfrequency coil to be gradually moved further downwards so as to ensure gradual. cooling of the window.

Ihe method according to the invention furthermore has the advantage that the. high-frequency current need not be controllable accurately but may be adjusted to a. given strength during the sealing process. Consequently, the heating of the glass need not be controlled by gradual intensification of the high-frequency field but is controlled exclusively by means of the position of the high-frequency coil with respect to the cone and the sealing edge 6. The highirequency equipment may thus be simpler, whilst controlling the temperature of the window by moving the coil 5 is considerably simpler than manual readjustment of the high-frequency current for controlling the temperature of the window.

Finally, a glass tube 8 is sealed in the conventional manner to the narrow extremity of the cone, said tube being closed by a base 9 which carries an electrode system l0 (see Fig. 2).

The invention is suitable more particularly for sealing windows of large diameter, for example 40 to cms., and a thickness of the. glass of from 4' to 10 mms. The high-frequency coil may have a diameter of approximately cms. and may consist of six turns of copper tubing in which a cooling liquid may circulate, as is common prac tice.

It is evident that the arrangement of the equipment for carrying out the method according to the invention may differ from that which is shown.

What we claim is:

1. A method of sealing a glass window to the open end of a metallic cone for a cathode-ray tube comprising the steps of surrounding the window with a heat radiating screen, surrounding a portion of the metallic cone remote from the window with a coil excited by a high-frequency electric current to induce a localized zone of heat in said metallic cone, and moving the coil longitudinally relative to the cone in the direction of the window thereby displacing the heating zone towards the window so that the window is heated by radiation from the cone to an extent at which the edge of the window is sealed to the cone when the heating zone has reached the sealing edge of the cone.

2. A method as claimed in claim 1, in which the heat radiating screen has a curvature simi lar to that of the glass window.

3. A method as claimed in claim 1, in which the heat radiating screen has a reflecting surface at least on the side remote from the window.

JOHANNES GIJSBERTUS WILHELM MULDER. THEODORUS HAGENBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name 'Date 1,301,714 Kueppers Apr. 22, 1919 2,048,556 McArthur July 21, 1935 2,296,307 Power Sept. 22, 1942 2,359,501 White Oct. 3, 1944 

